The invention relates to a process for guiding the excavation tool used for the construction of a wall cast in the ground, and also to a useful modified excavation tool for implementing this process.
Walls cast in the ground are executed by alternating or successive elementary panels. The finished work therefore consists of a succession of unitary panels whose geometrical continuity it is imperative to be able to guarantee in the course of execution.
In order to achieve this geometrical continuity of execution, two methods are used independently or jointly.
The first consists in giving to the excavation tools (mechanical or hydraulic grabs in the case of a discontinuous excavation and extraction of the spoil, or cutters with bull wheel or with chains, or rotary cutters in the case of a continuous excavation and extraction) a body of great height and of cross section very close to the cross section of excavation, so as to produce, in conjunction with the lowering of the center of gravity, a self-guiding on the excavation per se in the course of execution. Monitoring and correction devices may be incorporated in the excavation tools so as to correct more or less effectively any possible deviation with respect to the nominal trajectory.
The second consists in guiding the excavation tool more or less effectively in relation to the panel previously executed. In the conventional wall execution method in very general use a shuttering is put in place at the panel end before concreting is extracted as a sliding shuttering before the concrete has completely set. The gap thus made enables a certain guiding of the excavation tool to be ensured at the time of execution of the following panel.
These fairly approximate methods of guiding are acceptable only in the case of the construction of cast walls of relatively small depth.
Now, the use of cast walls for the construction of Civil Engineering Works at increasing depths (possibly in excess of 100 meters for example) and in increasingly difficult terrain has created the need for a technology of execution which makes it possible to guarantee a priori the geometry and the continuity of the constituent elementary panels. The currently available solutions which are acceptable down to a certain depth are unsatisfactory for deeper works or works requiring a higher degree of safety.
Furthermore, European Patent No. 0,101,350 describes a specific process for extraction of the end shuttering by removing the lateral shuttering which also enables the effective guiding of the excavation tool to be ensured at the same time. However the guiding function of this device is subordinate to its simultaneous shuttering removal, the primary subject of the invention described. In addition, this guiding process is based fundamentally on the sliding of two members, the one in the other. Experience shows that its correct functioning, despite which the risks of jamming and of final locking are not completely avoided, requires a dynamic operation, for example by to-and-fro movement or driving of the excavation tool, given the adverse conditions constituted by the medium heavily loaded with solid particles in suspension coming from the ground in which the entire assembly is immersed. This system is therefore well suited to the case where grabs are used as the excavation tool, but is less suitable in the case where continuous excavation tools such as wall cutters are used.